I think this is more of a rough but accurate to a degree estimate study more than a 100% completely accurate study. I would expect nothing more.

Just from looking at those charts, there is no denying RNC's are more used than armbars and these are the 2 dominant submissions, which can put to rest some arguments in regards to which ones are the most common and which is the most common.

It does answer questions as the OP has intended and he has also pointed out it is not uber accurate, so take it as it is.

i find it hard to believe there are only 4 keylocks in ufc history (although i'm sure it is a low number)... gonzaga definitely tapped mccully with a keylock (it's listed on sherdog as a kimura).

There are more than 4. Off the top of my head Steven Graham tapped Dmitri Stepanov by keylock. Sherdog has it listed as "Armlock"; Wikipedia has it listed as "Submission". Severn tapped Dave Beneteau by the same (thanks to the Tripps). Whch are the 4 you counted?

Now darkness comes; you don't know if the whales are coming. - Royce Gracie

from a research standpoint should you be including all the ufcs that have happened? i mean early ufc (1-20) was really style vs style, when is the point in time you would describe as mma became a discipline in itself and was pumping out credible fighters from credible coaches? shouldnt you be taking your data from that point onwards?

Some line graphs tracing out which submissions have become more/less popular over time would be cool.

I considered doing that, and still may. But it would only work for the top few submissions, and even then the graphs wouldn't be that enlightening. There is a lot of variation here. In a year where there are 50 submissions, a mere 5 subs counts for 10% of the total. Because the number of submissions isn't very high from a statistical point of view, a line graph would fluctuate very widely from event to event, and probably wouldn't show a clear trend. Graphing it vs time has a problem too, that since 2005 there have been far more events (and subs) in a year than years before that. A graph by time would be very erratic for the first 14 years, only becoming more stable in the past 3 or so.